1. Field of the Invention
The present invention relates to a light-emitting device with the use of a light-emitting element in which a film including an organic compound (hereinafter, referred to as an “organic compound layer”) disposed between a pair of electrode is provided fluorescence or phosphorescence by applying an electric field, and a method for manufacturing the light-emitting device. A light-emitting device in the present specification may include an image display device, a light-emitting device, or a light source (including a lighting system). In addition, a module that a connector, for example, a FPC (Flexible Printed Circuit), a TAB (Tape Automated Bonding) tape, or a TCP (Tape Carrier Package) is installed in the light-emitting device, a module that a printed wiring board is provided at an end of a TAB tape and a TCP, and a module that an IC (integrated circuit) is mounted directly in the light-emitting device by a COG (Chip On Glass) method are all included in the light-emitting device.
2. Description of the Related Art
In recent years, research related to a light-emitting device having an EL device as a self-luminous light-emitting device has been activated. The light emitting device is also referred to as an organic EL display or an organic light-emitting diode. Since these light-emitting devices have characteristics such as rapid response speed that is suitable for a moving picture display, low voltage, low power consumption driving, they attracts an attention for next generation displays including new-generation mobile phones and portable information terminals (PDA).
The EL device comprises an anode, a cathode, and a layer containing an organic compound generating luminescence (electroluminescence) by applying an electric field (hereinafter, referred to as an EL layer). As luminescence generated in an organic compound, there are luminescence (fluorescence) generated by reverting an excited singlet state to a ground state and luminescence (phosphorescence) generated by reverting an excited triplet state to a ground state. The luminescence radiation is allowed to take place by reverting from either state to the ground state in the light-emitting device manufactured by a fabrication system and a film forming method according to the present invention.
The light-emitting device has no viewing angle difficulty for its self-luminous property differently from a liquid crystal display device. Thus the light emitting device is more suitable for using at outside than the liquid crystal display device. Various types of usage are proposed for the light-emitting device.
In the specification, a light-emitting element formed of a cathode, an EL layer, and an anode is referred to as an EL element. There are two kinds for forming the EL device; a simple matrix that an EL layer is formed between two kinds of striped electrodes being perpendicular to each other, or an active matrix that an EL layer is formed between a pixel electrode and a counter electrode arranged in matrix that are connected to a thin film transistor (hereinafter: TFT). When a pixel density is increased, the active matrix is considered to have an advantage over the simple matrix because the active matrix can drive at low voltage for having a switch in each pixel (or each dot).
Conventionally, an organic EL element that a thickness of a layer including an anode and a plurality of organic compounds is set so that predetermined wave length of light provided from an EL layer becomes peak wave-length is disclosed, for example, in light-emitting device having luminescence transmitted in a cathode and luminescence transmitted in an anode from three light-emitting devices (red, green, and blue) that materials of a cathode and an anode are transparent, wherein each of luminescence transmitted in a cathode and luminescence transmitted in an anode are the same in color coordinate.
The luminescence transmitted in a cathode and an anode passes various layers or substrates. For example, in the case of an active matrix type light-emitting device, number of laminated layers to be passed from a luminous point are different because a switching device such as a TFT is disposed on a cathode side or an anode side and an interlayer insulating film (a silicon nitride film and an organic resin film) of a TFT is formed on a cathode side or an anode side. When a sealing substrate is pasted to a device substrate, a distance from a luminous point to an element substrate and a distance from a luminous point to the surface of the sealing substrate surface are also different. These factors cause a difference in a color tone of luminescence.
The present invention realizes a light-emitting device providing both luminescence to a top surface and luminescence to a bottom surface with an image display having an uniform color tone and high quality by adjusting a film thickness of a transparent conductive film and a film thickness of a cathode.
Constitution of the invention disclosed in the present specification provides a light-emitting device comprising: a pixel portion having a plurality of light-emitting elements of three kinds (red, green, and blue) having a transparent first electrode, a layer including an organic compound over the first electrode, and a transparent second electrode over the layer including the organic compound, wherein luminescence of three colors of red, green, and blue form the same triangles in a color coordinate as for both luminescence passing a first electrode and luminescence passing a second electrode. Reference 1. (Reference 1: Japanese Patent No.2846571)
When materials of a cathode and an anode are transparent and a substrate and a sealing substrate are transparent, luminescence from a layer including an organic compound can simultaneously perform two ways of display: luminescence transmitted in a cathode and luminescence transmitted in an anode.
However, the difference in optical characteristics (such as a color tone) between luminescence from a top surface and luminescence from a bottom surface arise for an interference effect by a difference of an optical distance. When a light-emitting device (an EL device) of three kinds (red, green, and blue) that materials of a cathode and an anode are transparent is used to manufacture a light-emitting display device of full color, problem that a color coordinate is different between luminescence from a top surface and luminescence from the bottom surface arises as shown in FIG. 8. If a color coordinate is different, the same gradation display in the top surface and the bottom surface is impossible.
A film thickness of such as an anode, a cathode, a protective film, and a layer including an organic compound in RGB is required to be controlled respectively in the case of full color, because an optical distance is different depending on each wavelength.